What Kit do I Need to Replace My Dometic Duo Therm with a New Advent Set-Up?

Updated 07/15/2026 | Published 07/04/2026

Question:

Hi, I would to replace my old Dometic Duo Therm model: 620425.331 product 991 740 399 by an ASA Advent ACM 135 but like you can see it is hardwired no plug. What will be my best option? Thanks

asked by: Michel P

Dometic Duo Therm Installed
(click to enlarge)

Expert Reply:

Hello Michel,

Thanks for writing in, and the pictures are always a nice bonus!

Based on the information in your photos, it looks like your current AC system uses the older R410A refrigerant. Since RV manufacturers have transitioned to the newer R32 refrigerant, the new R32 components are not compatible with the older R410A components. Because of that, you'll need to replace the complete system rather than just the rooftop unit.

I recommend the Advent Air RV AC System with Wall Thermostat # ADV95SR. This complete system includes the rooftop AC, air distribution box, wall thermostat, wiring harness, start capacitor, mounting hardware, and roof gasket, so you'll have everything you need to make the conversion to the new R32 refrigerant. It can be installed in either a ducted or non-ducted application, making it a great replacement for your existing setup.

Since this is a complete system, you won't be reusing your existing air distribution box or thermostat. The new wiring harness and wall thermostat included with the kit replace the older R410A components, so there isn't a need to try to adapt the new unit to your existing controls. That makes the installation much more straightforward and eliminates any compatibility concerns between the old and new systems.

If your current rooftop unit is hardwired, the new system will be wired according to the included installation instructions. If it's currently connected with a plug, that plug is part of the older system and won't be reused with the new R32 components.

Getting things geared up to stay cool on the next adventure? Where are you headed to next?

expert reply by: Kate F

Michel P.

7/6/2026

Thanks Kate for your valuable advice! I counted 11 cables coming from the roof connected to my A/C unit, in addition to the 120V cables. I imagine the ones from the roof are connected to the furnace, thermostat, etc. I'd like to know if I can reuse these same cables with the new wiring harness and also to the new thermostat, etc. Thanks I just want to be sure before I stat this project! I don't want to have to run any more cables :-) Michel

Kate F.

7/6/2026

@MichelP The good news is you should not have to run a new 120V power cable. The existing AC power wiring that feeds your current rooftop unit is typically reused with the new Advent system. In many cases, the existing low-voltage thermostat wiring can also be reused, so you aren't starting from scratch. The new Advent control box and thermostat replace the old Coleman components, and the existing control wires are connected to the new system based on their function rather than simply matching wire colors. The old control box, thermostat, and their connectors will be removed and replaced with the new Advent components that come in the kit. The key is identifying what each existing wire does before making the new connections.

Michel P.

7/6/2026

@KateF Thank you Kate, The new Advent control box and thermostat replace the old Coleman components and Dometic Duo Therm, 620425.331 like my old A/c unit? Last Question, is the Advent ACM135 will do the same as the ACR135 with the ACRDTH25 plus the start Capacitor. Michel

Kate F.

7/7/2026

@MichelP Yes, out with the old and in with the new. I can see your confusion with the other part numbers, it is also an out with the old in with the new. The ACM135 is for the old R410a refrigerant, you don't want that, you want the new R32. Once the R410a's are gone, they are gone for good and you cannot mix the parts. The # ADV95SR will come with the ACR135 which is the new R32 refrigerant, wall thermostat, air distribution box, and start capacitor.